GMC Truck:

1939 to 1959 GMC Truck Serial Number Information – From OldGMCTrucks.com is the great collection of hard to find GMC Truck parts book serial number decoding pages.

1935 to 1959 Canadian Built GMC Truck Serial Number Information – From the same site is this collection of even harder to find Canadian specific serial number information.

1955 to 1959 GMC Truck Identification Guide – A manual serial number and series guide for US built examples.